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The ergonomic advantages of using handrests for microneurosurgery

IM Greenberg
1 July, 2006  

IM Greenberg
MD PC
Diplomat
American Board of Neurological Surgery

The term ergonomics was coined in the mid-20th century by KFH Murrell and his colleagues in the UK to describe studies of human performance in relation to machines and their environment. Ergonomics refers to the natural laws – “nomos” – of work or “ergos”. Ergonomic analysis of a neurosurgical procedure can encompass a range of variables. These include:

  •  The neurosurgeon’s sensory perception of the surgical field and its anatomic structures.
  • The surgeon’s posture and position while operating.
  • The demands made upon the surgeon’s physical strength, dexterity, balance and endurance.
  • The length of a procedure.
  • The design characteristics and efficiency of the surgical instruments used during the procedure, including the microscope.

There is a great variation in these elements – between surgical applications, neurosurgeons and the techniques in which these elements interact. These variations not only determine the difficulty or even feasibility of a procedure, but ultimately the success or failure of that operation.

Proprioception
Proprioception is the perception of body position by joint and muscle receptors, and the vestibular portion of the inner ear. It plays a major role in helping the surgeon to remain steady in a given position or to execute finely controlled movements. Maintaining a steady position and executing fine “motor” movements require varying degrees of muscular tension and relaxation. Stimuli produced in response to this tension are picked up by proprioceptor nerve terminals located in muscles, tendons and joints. These terminals receive information on movements and hand/body positioning, and feed this back to the surgeon’s receptor system as it seeks to attain the most stable and comfortable positions.

Fatigue
A lack of support for the surgeon’s hands, the resulting instability and fatigue are major contributors to the tremor that the standing surgeon experiences. Any method that surgeons can use to stabilise their positions will contribute to tremor reduction, while extending the period of peak performance. The observations of many neurosurgeons have revealed that support for the hands is highly desired. Surgeons operating without any support for hands and arms (“airborne”) are quickly subject to fatigue, strain and imprecise movements.
 
At present, the most widely employed technique for supporting hands is to rest fifth fingers just peripheral to the operating field. The major limitation of “pinky neurosurgery” is that this finger is the weakest. It is ill-suited to provide the degree of stability required when operating for extended periods of time under a microscope. The microscope additionally magnifies the imprecise, involuntary movements of instruments held by unsupported hands. The small size of the operating field, particularly the visual field seen though the microscope, simply leaves no room for such imprecise movements. Although this concept seems self-evident, our inheritance of macrosurgical approaches and techniques must be improved to keep pace with the surgical possibilities derived from using the microscope and our imaginations. The use of a handresting device is increasingly essential for preventing or reducing fatigue and achieving higher precision during precise, delicate dissection.

Hand stability
Recognition of the surgeon’s need for hand support and the availability of the pin headrest as a stable platform led to the creation of devices to support the surgeon’s hand surgery. Artists have solved the problem of hand support by using the maul stick, which dates back to the Byzantine tradition of the 13th century. In the surgeon’s case, such support would be placed as close to the operative sight as possible to reduce the movement arc of the tips of surgical instruments as they are used. This increases the surgeon’s control, improving the accuracy of instrument movements.

Airborne instruments without support
Figure 1 shows a procedure being performed without any support for the hands. This approach usually leads to a tremendous expenditure of energy and tension.

[[HHE06_fig1_T59]]

Perfection of ergonomic efficiency with the handrest
By contrast, Figure 2 is a perfect example of ergonomic efficiency. With the palm on the handrest, proprioceptive touch information is processed. The muscles of the forearm, arm, shoulders and neck can all relax. There is only tension between the thumb and index finger holding the instruments. Movements are executed by slightly flexing and extending these fingers with a little rotation at the palm.

[[HHE06_fig2_T59]]

Self-retaining retractors
Handheld retractors were in vogue until the mid-1970s. Mechanical retractor mounts have, however, been in use since the 1930s. In general, there are two categories of self-retaining retractors. One is mounted on the skull, with either direct contact to bone or tissue or indirect contact via a skull clamp (such as the Gardner or Mayfield). The other is mounted onto the operating table.

The staircase concept of surgical performance
When some highly articulated, pin headrest-mounted systems, such as the Greenberg system, began to enjoy widespread use in a variety of neurosurgical procedures, it quickly became apparent it was also necessary to formulate and describe specific principles. The ergonomic and proprioceptic knowledge and techniques that I have studied and applied over the past four decades has greatly influenced further development of this system.
 
The integrated surgical support system (ISSS) provides a variety of components that enable the surgeon to create a supporting framework for the mechanical support and navigation of retractor blades, suction tube, patty tray, microdissectors, fibreoptic illuminator, scissors and pneumatic drill, in addition to the hand support. The system is organised in three vertical levels, both structural and functional. Level I is located at the level of the operative field; its primary function is to support self-retaining retractors and micro-instruments. Level II is located directly above the operative field (Level I). It is purely functional and provides the two hand supports. The hand supports also function as a “parking place” for handheld instruments, such as the bipolar coagulator, during surgery. This simple but most practical addition to the retractor system offers: less tremor; less frustration; less fatigue; and better control in performing the delicate tasks required.

Level III is located above Levels I and II. It supports large instruments, such as the pneumatic drill, which are used intermittently. ISSS therefore provides an ergonomically sound solution: hand movements, position adjustments, changing of instruments, repositioning of retractors are all achieved within a small, organised and balanced field.